This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Major thrust of our research projects is to understand structure-function relationships in medically important viruses such as rotavirus (NIH AI36040), caliciviruses (NIH P01 AI57788-01 in collaboration with Dr. M.K. Estes), orthoreoviruses (NIH RO1 AI32539 in collaboration with Dr. T. Dermody), and influenza viruses (in collaboration with Dr. Andrew Rice, grant submission in progress). We have been using NCRR funded NCMI facility over years, and we will continue to use this excellent facility. The world-class high resolution imaging and image processing facilities are excellently suited for our projects. Rotavirus: Rotavirus is the major cause of severe, life-threatening gastroenteritis in young children and animals. Rotaviruses are large (1000 [unreadable] ), complex, icosahedral assemblies. This virus has been the subject of extensive biochemical, genetic and structural studies because of its medical relevance, intriguing structural complexity, and unique strategies of replication and morphogenesis. We will continue further understanding of the structural basis of rotavirus cell entry, endogenous transcription, viroplasm formation, genome replication and packaging at sub-nanometer resolution using the NCMI cryo-EM facility. Our focus will be particularly on human strains. While some of these studies involve rotavirus particles (1000 [unreadable] diameter), others that are related to viroplasm formation, genome replication/packaging involving rotavirus non-structural proteins such as NSP2, NSP5, VP1, VP2 and NSP6. In infected cells, these proteins work in concert during viroplasm formation, genome replication/encapsidation. To obtain structural insights into how these rotavirus proteins function, high-resolution cryo-EM analysis is perhaps the only option. Caliciviruses: Caliciviruses, grouped into four genera, are important human and veterinary pathogens with a potential for zoonosis2. In these ssRNA viruses, capsid related functions such as assembly, antigenicity, and receptor interactions are encoded in a single protein that forms an icosahedral capsid. We are interested in obtaining structural information about members of the Caliciviridae. We will continue to use NCMI facility to investigate calicivirus-receptor, and calicivirus-antibody interactions. In addition, we plan to use these resources available at NCMI for characterizing norovirus p41 protein that exhibits helicase/NTPase activities. Noroviruses are causative agents of epidemic diarrhea in humans 3. Orthoreoviruses: The goal of the proposed research is to determine mechanisms of non- enveloped virus internalization, disassembly, and membrane penetration using mammalian reovirus as an experimental system. We will continue to use NCMI facilities to further investigate structural basis for reovirus disassembly and membrane penetration by determining structures of sequential reovirus disassembly intermediates, and that of reovirus mutants selected during persistent reovirus infection (PI viruses), which demonstrate enhanced in vitro kinetics of disassembly and grow in the presence of inhibitors of endosomal acidification (ammonium chloride)4 and proteolysis. Influenza virus NS1 protein: Recent emergence of highly pathogenic avian (H5N1) influenza viruses, their epizootic and panzootic nature, and their association with lethal human infections have raised significant global health concerns. Several studies have underscored the importance of non-structural protein NS1 in the increased pathogenicity and virulence of these strains. NS1, is an antagonist of antiviral type-I interferon (IFN) response in the host.